There are known methods and systems for real-time transfer of data between a central station and a plurality of peripheral stations, which are based on the utilization of multiplex communication channels. The major disadvantage of such methods and systems is a low channel utilization factor, keeping in mind that the throughput of a channel is 0.184 to 0.5 Erl, while the rated traffic load is between 0.05 and 0.20 Erl. It is thus very expensive to build and operate a sufficient number of such channels.
In recent years, there has been intensified utilization of computers and automatic control, monitoring, dispatching, information and data teleprocessing systems of different classes in industry, transport, construction, trade and other fields. It is therefore essential to make multiplex channels cheaper and more effective in order to render computer systems accessible to terminals scattered over vast territories, as well as to remote and mobile terminals. There is another important aspect to this problem. Apart from being inexpensive, the data transmission channels and equipment must feature a high reliability and noise immunity in order to ensure effective real-time data transmission.
A method for an exchange of data between a central station and peripheral stations is known and is described, for example, in U.S. Pat. No. 2,226,778 of the Federal Republic of Germany, which issued Apr. 10, 1975. In the method of the German patent, an address signal is produced at the central station, which is a two-level signal with address bit values of "1" or "0," which follow one another at equal intervals.
The combination of such levels and intervals carries information on the address bits, information on the synchronization of address bit periods, and information on the synchronization of a specified number of data bit periods in the form of regular sequences.
Thus, an address signal is a periodic address sequence. The elements of this sequence are to meet a predetermined recurrence relation. The address sequence includes M non-recurrent subsequences which designate the addresses of the selected peripheral stations. There is a partial overlapping of subsequences designating the addresses of two peripheral stations next to each other.
Certain elements of the address sequence and elements intended for data transmission are then used to form elementary address signals and elementary data signals. When calling on each next-successive peripheral station, only those elementary address signals are sent into the channel which correspond to the non-overlapping part of the subsequence, designating the address of the next peripheral station. At each peripheral station, synchronizing address pulses and elements of the sequence being generated are separated from the address signal. This is followed by accumulating the separated elements of the sequence being generated and producing a subsequence of these elements, whereupon the subsequence of elements thus produced is compared with the address of the given peripheral station. An exchange of data can be effected when the accumulated subsequence of elements coincides with the address of the given peripheral substation. The address signal is modulated by at least one of the peripheral stations or by the central station. At least one data bit is used to synchronize data pulses. The information on the data pulses is contained in the equal transition intervals of the two-level address signal. There is a set number of equal transition intervals in each elementary address signal. The elementary address signals are transmitted in a certain order regardless of the presence or absence of data for each peripheral station. This means that the synchronizing address pulses and synchronizing data pulses form regular sequences. At least at one selected peripheral station, the address of which coincides with the data address, or at the central station, the address signal is demodulated by the synchronizing pulse of the given address and the synchronizing data pulse, respectively.
A system for an exchange of data between a central station and peripheral stations is also known. The known system comprises a recurrence sequence generator installed at the central station and intended to produce an address signal as a sequence whose elements are in keeping with a predetermined recurrence relation and which includes M non-recurrent subsequences designating the addresses of the selected peripheral stations. The recurrence sequence generator is connected to a first input of a code addressing unit whereof a second input serves as a data address input. A first output of the code addressing unit is an address output of the central station.
The equipment of the central station includes a data input register whose input is an information input of the central station and whose output is electrically coupled to a transmitter which is also connected to the recurrence sequence generator. The central station also incorporates a data output register whose output is an information output of the central station and whose input is electrically coupled to a receiver. An output of the transmitter and an input of the receiver are a signal output and signal input, respectively, of the central station. The central station also has a synchronizing pulse generator.
Each of the peripheral stations has a receiver electrically connected to a data output register, and a transmitter electrically connected to a data input register.
Each peripheral station includes a synchronized regular pulse generator whose input is connected to the output of the receiver, and a recurrence sequence filter connected to an address selector, a synchronizing address pulse discriminator and the receiver. The output of the data output register and the input of the data input register are an information output and an information input, respectively, of the peripheral station. The input of the receiver and the output of the transmitter are a signal input and an output, respectively, of the peripheral station.
The synchronizing input of the recurrence sequence generator is connected to an output of a regular pulse sequence generator. The recurrence sequence filter is a passive element, constructed as a shift register.
The known method includes generating two-level address signals comprising regular sequences of synchronizing address pulses and synchronizing data pulses. This means that specified periods of time are separately allotted for the reception and transmission of data to each peripheral station irrespective of the presence or absence of data for transmission from a given peripheral station to the central station and back. The stream of data is of a random nature, wherefore peripheral stations only use a small part of the periods of time allotted to them. This affects the utilization factor of the multiplex channel. The throughput of the channel is limited, and it caters to a limited number of peripheral stations. It also takes much time to transmit data. The foregoing factors account for high costs of data transmission. According to D. R. Doll, "Multiplexing and Concentration Computer Communications", ed. by P. E. Green and R. W. Lucky, Proc. of the IEEE, vol 60, No. 11, November 1972, NY, USA, typical peripheral stations use less than 10 percent of the alotted time, wherefore the channel traffic load is less than 0.1 Erl.
Furthermore, the known method is not free from errors in the addresses. This is due to the fact that the system, whereby the method is carried out, uses passive recurrence sequence filters and non-recurrent address subsequences, as well as due to the fact that the data being transmitted do not include the address of a given peripheral station.
An object of the present invention is to provide a method for an exchange of data between a central station and peripheral stations and a system for effecting same, which increases the throughput of the multiplex channel.
Another object of the invention is to provide a method for an exchange of data between a central station and peripheral stations and a system for effecting same, which permits an increase in the number of peripheral subscriber stations.
Still another object of the invention is to provide a method for an exchange of data between a central station and peripheral stations and a system for effecting same, which speeds up the real-time transmission of data through multiplex channels.
Yet another object of the invention is to provide a method for an exchange of data between a central station and peripheral stations and a system for effecting same, which reduces the costs of data transmission.
A further object of the invention is to provide a method for an exchange of data between a central station and peripheral stations and a system for effecting same, which ensures a high accuracy of data transmission.